The present invention relates to a golf club that has a face wall which allows the club head to be made larger than other methods of construction without adversely increasing club head weight, while retaining adequate strength and large moments of inertia.
It has been recognized that a larger size of a golf club face is an important advantage to a golfer. With a large face club, it is much easier to avoid hits which are partly off the club face, and a large face allows the club head to be designed to achieve large moments of inertia of the club head, which reduces the errors due to off-center hits.
In the prior art, there have been golf clubs known as "woods" which have been made with solid wood heads, and in some instances these have been faced with plastic, but only when the plastic layer is the front portion of an essentially solid block of wood. At present, most clubs called woods are made as a thin metal shell in two or three parts and a face wall, which are welded together. Aluminum, stainless steel and titanium have been used.
Layers of material that are said to be an advantage have been placed on the front face of a wood club. For example, a layer of titanium cemented into a shallow recess in the face of a stainless steel club head is known. Thin layers of a plastic or rubber-like material have been used on the front surface of putters to form a softer surface, but they supply only a minor part of the strength of the face.
A golf club "wood" is shown in U.S. Pat. No. 5,380,101, which has a hollow head reinforced with a structural element, wherein the face is made of the known materials, including fiberglass reinforced plastic. A golf club shown in U.S. Pat. No. 1,485,685 has a shell type head with wood plugs reinforcing the face in selected locations. Various other types of veneers or synthetic resins also have been used.
U.S. Pat. No. 5,366,223, is also referred to for a showing of orienting a club face for agreement between a hit pattern and a club face perimeter. For a hollow or shell design, a large size allows weight of the club head to be spaced farther from the center of gravity. The moment of inertia about any particular axis of rotation is the summation of each of the mass elements times the square of its distance from the axis of rotation. Thus, the larger size increases the moment of inertia about any axis which may be chosen. This is true even when the wall thickness is somewhat reduced in a hollow head to maintain a given head weight. The large size is beneficial to the golfer because when the ball is hit off center, the club head rotates slightly during impact and disturbs the shot. The magnitude of this disturbance is highly dependent on the moment of inertia about the axis of rotation. Increasing the moment of inertia decreases the errors caused by off-center hits.
One of the criteria for good club design is that the head weight should be kept reasonably near its optimum value. This is about 190 grams for a modern 46 inch shaft. The maximum distance of a drive will be reduced if the head weight is too large or too small. In prior art designs, the face size is limited to a maximum size of 5.21 square inches, which is the largest size found in a survey, sold by Golfsmith International under the trademark "Long Jon". The reason is that this requires the face to be too heavy in order to support the load of impact of ball and club face. This impact load can exceed 3,000 pounds.